几何构型对流动聚焦生成微液滴的影响

流动聚焦型微流控装置能够方便、高效地生成均一度好且大小精确可调的微液滴(气泡)，故被广泛应用于颗粒材料合成、药物封装、细胞培养等诸多领域. 进一步优化通道结构有助于实现对合成微粒粒径、均一度和尺寸范围的精确调控. 本文数值研究了通道深度、缩颈段长度以及两相夹角等几何构型因素对流动聚焦生成微液滴直径及其生成周期各个阶段的影响. 控制液滴生成方式为滴流式，发现液滴直径随通道深度d 的增加近似呈线性增大，且当通道深度小于30 μm 时，随着通道深度的下降，微液滴生成周期在毛细力的强烈作用下出现骤升，通道深度超过80 μm 时，微液滴的生成周期基本接近恒定. 连续相和离散相的夹角θ接近90°时，液滴直径及其生成周期最短，夹角太大或太小均不利于生成均一度好且粒径微小可控的液滴. 调整缩颈段长度l引起液滴直径及其生成周期的变化幅度仅为其平均值的3%~5% 左右. 此外，缩颈段宽度也是影响流动聚焦生成微液滴直径及其生成周期的重要因素，在通道深度固定时，缩颈段越宽，微液滴直径及其生成周期越大. 

INFLUENCE OF GEOMETRY CONFIGURATIONS ON THE MICRODROPLETS IN FLOW FOCUSING MICROFLUIDICS

Micro flow-focusing devices were widely used in the synthesis of particulate material, drug packaging, cell culture and other areas owing to the convenience and effectiveness to produce highly monodisperse and precisely sizecontrollable droplets. To optimize the channel structure and geometry parameters deeply is of benefit to achieve the precise regulation of droplets' diameter, uniformity and the size ranges. For the adaptive design, channel depth, orifice length and the angle in continuous and discrete phase are taken into account to investigate the influence of geometry configurations on the microdroplet diameter and its generated cycle stages in flow focusing microchannel by making use of numerical simulation. It is shown that the droplet diameter approximately increases linearly with the channel depth, meanwhile, when the channel depth is less than 30 μm, the droplet's cycle increases suddenly under the application of strong capillary force. The microdroplet diameter and its cycle are both the shortest while the angle of the continuous phase and discrete phase θ is nearly 90°, and too large or too small angles are both not conductive to generate droplets with uniform diameter and well controlled particle size. Orifice length is used to adjust the alteration of the microdroplet diameter and its cycle, which lead to the average rangeability within 3%~5%. In addition, the width of orifice region is an important factor a ecting the microdroplet diameter and its cycle in cross microchannel. When the channel depth is fixed, the wider the orifice region is, the greater the microdroplet diameter and its cycle are.